Packaging material consisting of an at least double-layered composite material for producing containers for packing liquids

ABSTRACT

Packaging material comprises an at least two-layer laminate of a paper engine-sized in each case with a polymer size or sized cardboard and at least one water-impermeable film or foil for producing containers for packaging liquids, and paper products which are obtainable in each case by (i) engine sizing of a paper stock comprising an aqueous slurry of cellulose fibers with at least one polymer size or with a polymer size and an aqueous dispersion of an alkylketene dimer or a mixture thereof in the presence of a retention aid and, if appropriate, of a water-soluble aluminum compound and, if appropriate, at least one cationic polymer, (ii) drainage of the paper stock on the wire of a paper machine, (iii) drying of the paper product and (iv) lamination of the paper product on one or both sides with a plastics film or metal foil are used for producing containers for packaging liquids, in particular beverages.

The present invention relates to a packaging material comprising an atleast two-layer laminate of sized paper or sized cardboard and at leastone water-impermeable film or foil for packaging liquids, and to the useof paper products which have been engine sized and which have beenlaminated on one or both sides with a plastics film or metal foil, forproducing containers for packaging liquids, in particular beverages.

EP-B-0 292 975 discloses the use of an emulsion of an alkylketene dimerin combination with a cationic rosin size and an agent impartinginsolubility, such as alum, for producing cardboard for packagingliquids. The cardboard is produced by adding size and alum to an aqueousslurry of cellulose fibers and draining the paper stock on a wire.

EP-A-1 091 043 discloses a process for producing a coated packagingcardboard, an aqueous slurry of cellulose fibers being engine sized withan aqueous dispersion of a rosin size, a synthetic size, such asalkylketene dimer, and at least one aluminum compound and the aqueousslurry being drained on a wire. The aqueous dispersions of engine sizescan, if appropriate, comprise a dispersant, e.g. cationic starch,casein, cellulose derivatives, polyvinyl alcohols, polyacrylamides orpolyethylenimines. The cardboard is usually coated after the sizing.

Paper products laminated on both sides with a liquid-impermeable layerand intended for packaging foods are disclosed in WO-A-02/090206. Thepaper products are engine sized with aqueous dispersions of alkylketenedimers. The amount of alkylketene dimers is at least 0.25, preferably0.25-0.4, % by weight, based on the weight of the dry paper products.

Further multilayer packaging materials whose base layer consists ofpaper or cardboard are described, for example, in WO-A-97/02140,WO-A-97/02181 and WO-A-98/18680.

The prior art also discloses the use of size mixtures comprising aqueousdispersions of alkylketene-dimers and polymer sizes for the enginesizing of paper and cardboard, cf. DE-A-32 35 529, WO-A-94/05855 andWO-A-96/31650.

The prior German application 10237913.0 discloses a process forproducing cardboard for packaging liquids. In this process, thecardboard is produced by engine sizing of an aqueous slurry of cellulosefibers with at least one engine size in the presence of at least oneretention aid and at least one cationic polymer and, if appropriate, awater-soluble aluminum compound and drainage of the paper stock on awire. Sizes described are alkylketene dimers, alkyl- and alkenylsuccinicanhydrides, alkyl isocyanates, combinations of rosin size and alum andcombinations of reaction products of rosin size with carboxylicanhydrides and alum.

It is an object of the present invention to provide further packagingmaterials based on paper products, where the packagings should have inparticular improved edge penetration and improved adhesion of thelaminates to paper or cardboard.

We have found that this object is achieved, according to the invention,by a packaging material comprising an at least two-layer laminate of asized paper or sized cardboard and at least one water-impermeable filmor foil for producing containers for packaging liquids, if the paper orthe cardboard is in each case engine sized with a polymer size.

The present invention also relates to the use of paper products whichare obtainable in each case by

engine sizing of a paper stock comprising an aqueous slurry of cellulosefibers with at least one polymer size as an engine size or with apolymer size and an aqueous dispersion of an alkylketene dimer or amixture thereof in the presence of a retention aid and, if appropriate,of a water-soluble aluminum compound and, if appropriate, at least onecationic polymer,

drainage of the paper stock on the wire of a paper machine,

drying of the paper product and

lamination of the paper product on one or both sides with a plasticsfilm or metal foil, for producing containers for packaging liquids, inparticular beverages.

All cellulose fibers usually used in the paper industry, for examplefibers of wood pulp and all annual plants, can be used for producingsized paper or sized cardboard. Mechanical pulp is understood asmeaning, for example, groundwood, thermomechanical pulp (TMP),chemothermomechanical pulp (CTMP), pressure groundwood, semichemicalpulp, high-yield pulp, refiner mechanical pulp (RMP) and wastepaper.Pulps which can be used in bleached or in unbleached form are alsosuitable. Examples of these are sulfate, sulfite and soda pulps.Unbleached pulps, which are also referred to as unbleached kraft pulp,are preferably used. The fibers may be used alone or as a mixture withone another.

In the engine sizing of paper or cardboard, sizing is carried out duringthe process for the production of these materials, by adding an enginesize to the paper stock and draining said paper stock on the wire of apaper machine with sheet formation. According to the invention, theengine size used is a polymer size comprising synthetic polymers. Thepolymer sizes disclosed in JP-A-58/115 196 are aqueous polymerdispersions which are a paper size and at the same time increase thestrength of paper. These dispersions are prepared by polymerization of,for example, styrene and alkyl acrylates in the presence of starch andfree radical polymerization initiators in an aqueous medium. The starchused in each case is digested or degraded before the polymerization, sothat it is soluble in water. The polymers of these dispersions are graftpolymers of styrene and alkyl acrylates on starch or modified starch.

Further polymer sizes are disclosed in EP-B-0 257 412 and EP-B-0 267770. They are prepared by copolymerization of acrylonitrile and/ormethacrylonitrile and at least one acrylate of a monohydric, saturatedC₃- to C₈-alcohol by an emulsion polymerization method in an aqueoussolution which comprises a degraded starch, in the presence of freeradical initiators, preferably hydrogen peroxide or redox initiators.The degraded starches have viscosities η_(i) of from 0.04 to 0.50 dl/g.Such starches are obtained, for example, in an oxidative, thermal,acidolytic or enzymatic degradation of a natural or cationically oranionically modified starch. Natural starches from potatoes, wheat,corn, rice or tapioca are advantageously used. An enzymatically degradedpotato starch is preferred. The degraded starches act as emulsifiers inthe copolymerizatiori of, for example, styrene and n-butyl acrylate inan aqueous medium. The aqueous solution in which the copolymerization iscarried out comprises, for example, from 1 to 25% by weight of at leastone degraded starch. For example, from 10 to 150 preferably from 40 to100, parts by weight of the abovementioned monomers are polymerized in100 parts by weight of such a solution. Instead of acrylonitrile and/ormethacrylonitrile, it is also possible to use styrene in thecopolymerization, cf. WO-A-94/05855. Aqueous dispersions of copolymershaving a mean particle diameter of, for example, from 50 to 500 nm,preferably from 100 to 300 nm, are obtained. These polymer dispersionsare presumably graft polymers of the monomers used in each case ondegraded starch.

Further polymer sizes based on copolymers of styrene and C₃- to C₈-alkyl(meth)acrylates are disclosed in WO 02/14393. They are prepared bycopolymerization of said monomers in an aqueous medium in the presenceof degraded starch and free radical polymerization initiators by atwo-stage process.

Other suitable polymer sizes are those aqueous polymer dispersions whichcan be prepared in the presence of synthetic polymeric protectivecolloids. They are obtainable, for example, by copolymerization of from2 to 32 parts of a mixture of

-   (a) styrene, acrylonitrile and/or methacrylonitrile,-   (b) acrylates and/or methacrylates of C₁- to C₁₈-alcohols and/or    vinyl esters of saturated C₂- to C₄-carboxylic acids and, if    required,-   (c) other monoethylenically unsaturated copolymerizable monomers    in aqueous solution in the presence of 1 part by weight of a    solution copolymer of-   (1) di-C₁- to C₄-alkylamino-C₂- to C₄-alkyl (meth)acrylates which,    if appropriate, may be protonated or quatemized,-   (2) nonionic, hydrophobic, ethylenically unsaturated monomers, in    these monomers, if they are polymerized by themselves, form    hydrophobic polymers, and, if appropriate,-   (3) monoethylenically unsaturated C₃- to C₅-carboxylic acids or    their anhydrides, the molar ratio of (1): (2): (3) being 1:2.5 to    10:0 to 1.5, copolymerized.

First, a solution copolymer is prepared by copolymerizing the monomersof groups (1) and (2) and, if appropriate, (3) in a water-miscibleorganic solvent. Suitable solvents are, for example, C₁- toC₃-carboxylic acids, such as formic acid, acetic acid and propionicacid, or C₁- to C₄-alcohols, such as methanol, ethanol, n-propanol orisopropanol, and ketones, such as acetone. Preferably used monomers ofgroup (1) are dimethylaminoethyl acrylate, dimethylaminoethylmethacrylate, dimethylaminopropyl methacrylate and dimethylaminopropylacrylate. The monomers of group (1) are preferably used in protonated orin quaternized form. Suitable quaternizing agents are, for example,methyl chloride, dimethyl sulfate and benzyl chloride.

Monomers of group (2) which are used are nonionic, hydrophobic,ethylenically unsaturated compounds which, if they are polymerized bythemselves, form hydrophobic polymers. These include, for example,styrene, methylstyrene, C₁- to C₁₈-alkyl esters of acrylic acid ormethacrylic acid, for example methyl acrylate, ethyl acrylate, n-propylacrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate andisobutyl acrylate, and isobutyl methacrylate, n-butyl methacrylate andtert-butyl methacrylate. Acrylonitrile, methacrylonitrile, vinylacetate, vinyl propionate and vinyl butyrate are also suitable. Mixturesof the monomers of group (2) can also be used in the copolymerization,for example mixtures of styrene and isobutyl acrylate. The solutioncopolymers serving as an emulsifier can, if appropriate, also comprisemonomers of group (3) incorporated in the form of polymerized units, forexample monoethylenically unsaturated C₃- to C₅-carboxylic acids ortheir anhydrides, e.g. acrylic acid, methacrylic acid, itaconic acid,maleic acid, maleic anhydride or itaconic anhydride. The molar ratio(1): (2): (3) is 1:2.5 to 10:0 to 1.5. The copolymer solutions thusobtained are diluted with water and serve in this form as a protectivecolloid for the polymerization of the abovementioned monomer mixtures ofthe components (a) and (b) and, if appropriate, (c). Suitable monomersof group (a) are styrene, acrylonitrile, methacrylonitrile or mixturesof styrene and acrylonitrile or of styrene and methacrylonitrile.Monomers of group (b) which are used are acrylates and/or methacrylatesof C₁- to C₁₈-alcohols and/or vinyl esters of saturated C₂- toC₄-carboxylic acids. This group of monomers corresponds to the monomersof group (2) which are described above. Preferably used monomers ofgroup (b) are butyl acrylate and butyl methacrylate, e.g. isobutylacrylate, n-butyl acrylate and isobutyl methacrylate. Monomers of group(c) are, for example, monoethylenically unsaturated C₃- to C₅-carboxylicacids, acrylamidomethylpropanesulfonic acid, sodium vinylsulfonate,vinylimidazole, N-vinylformamide, acrylamide, methacrylamide andN-vinylimidazoline. From 1 to 32 parts by weight of a monomer mixture ofthe components (a) to (c) are used per part by weight of the copolymer.The monomers of the components (a) and (b) can be copolymerized in anydesired ratio, e.g. in a molar ratio of from 0.1:1 to 1:0.1.

The monomers of group (c) are, if required, used for modifying theproperties of the copolymers.

Sizes of this type are described, for example, in EP-B-0 051 144, EP-B-0058 313 and EP-B-0 150 003.

Preferably used polymer sizes are aqueous polymer dispersions which areobtainable by copolymerization of

from 20 to 65% by weight of styrene, acrylonitrile and/ormethacrylonitrile,

from 80 to 35% by weight of acrylates and/or methacrylates of monohydricsaturated C₃- to C₈- alcohols and

from 0 to 20% by weight of other monoethylenically unsaturatedcopolymerizable monomers, such as acrylamide, methacrylamide,vinylformamide, acrylic acid, methacrylic acid, maleic acid, itaconicacid, 2-acrylamido-2-methylpropanesulfonic acid or basic monomers, suchas dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,dimethylaminopropyl acrylate or dimethylaminopropyl methacrylate, thebasic monomers generally being used in the form of hydrochlorides or ina form quaternized with methyl chloride, dimethyl sulfate or benzylchloride, in the presence of free radical initiators by an emulsionpolymerization method in an aqueous solution of a degraded starch as aprotective colloid.

Other preferably used polymer sizes are aqueous polymer dispersionswhich are obtainable by copolymerization of

from 60 to 90% by weight of styrene and/or methylstyrene,

from 10 to 40% by weight of 1,3-butadiene and/or isoprene and

from 0 to 20% by weight of other monoethylenically unsaturatedcopolymerizable monomers, such as acrylic acid, methacrylic acid,itaconic acid, acrylamide, methacrylamide or N-vinylpyrrolidone,

in the presence of free radical initiators by an emulsion polymerizationmethod in an aqueous solution of a degraded starch as a protectivecolloid.

The polymer sizes are preferably cationic or anionic. The charge of theaqueous dispersions is based either on the type of comonomersincorporated in the form of polymerized units in the copolymers (forexample, the polymer size dispersion is cationic when basic monomers areused, whereas they are anionic as a result of incorporation of, forexample, acrylic acid or its salts in the form of polymerized units) oron the charge of the protective colloid used in each case. For example,the use of cationic starch as an emulsifier leads to cationic polymersize dispersions.

For the engine sizing of paper or cardboard, for example, from 0.1 to2.0, preferably from 0.2 to 0.75, % by weight, based on dry paperproduct, of polymer size (i.e. 100% strength polymer) are used.

The engine sizing of paper and cardboard can additionally be carried outin the presence of aqueous dispersions of reactive sizes, such asalkylketene dimers, C₅- to C₂₂-alkyl- and/or C₅- to C₂₂-alkenylsuccinicanhydrides, chloroformic esters and C₁₂- to C₃₆-alkyl isocyanates, andin the presence of combinations of rosin size and alum or ofcombinations of reaction products of rosin size with carboxylicanhydrides and alum. Instead of alum or in combination with alum, it ispossible to use other aluminum-comprising compounds, such aspolyaluminum chlorides or the polyaluminum compounds disclosed in EP-B-1091 043.

Among the reactive sizes, C₁₂- to C₂₂-alkylketene dimers, e.g.stearyldiketene, lauryldiketene, palmityldiketene, oleyldiketene,behenyidiketene or mixtures thereof, are preferably used.

Suitable succinic anhydrides are, for example, decenylsuccinicanhydride, octenylsuccinic anhydride, dodecenylsuccinic anhydride andn-hexadecenylsuccinic anhydride.

The reactive sizes are usually used in the form of an aqueousdispersion. For example, alkylketene dimers are dispersed in an aqueoussolution of a cationic starch, or nonionic or anionic emulsifiers areused for stabilizing the alkylketene dimers. The reactive sizedispersions formed are cationically or anionically charged or neutral,depending on the type and amount of the emulsifiers, or mixtures ofemulsifiers compatible with one another, which are used.

For example, anionic emulsifiers can be added to alkylketene dimerdispersions which were emulsified with the aid of cationic starch inwater. If the charge of the anionic emulsifiers predominates over thecharge of the cationic emulsifiers, an anionically charged alkyldiketone dimer dispersion is obtained. Anionically charged aqueousalkylketene dispersions are preferably prepared by emulsifyingalkylketene dimers in aqueous solutions of anionic emulsifiers. Forexample, condensates of naphthalenesulfonic acid and formaldehyde,sulfonated polystyrene, C₁₀- to C₂₂-alkylsulfuric acids, ligninsulfonicacid, phenolsulfonic acid, naphthalenesulfonic acid or the sodium,potassium or ammonium salts of said acids can be used as anionicemulsifiers. Copolymers of acrylic acid and maleic acid, homopolymers ofacrylic acid, homopolymers of methacrylic acid, copolymers of isobuteneand maleic acid and/or acrylic acid, hydrolyzed copolymers of isobuteneor diisobutene and maleic anhydride are also suitable emulsifiers forthe preparation of anionic alkylketene dimer dispersions. The acidgroups of the homo- and copolymers can, for example, be partly orcompletely neutralized with sodium hydroxide solution, potassiumhydroxide solution or ammonia and used in this form as anionicemulsifiers. The molar mass M_(W) of the homopolymers and of thecopolymers is, for example, from 1 000 to 15 000, preferably from 1 500to 10 000. The emulsifiers are used, for example, in amounts of up to3.5, preferably up to 2, % by weight, based on the reactive size to bedispersed.

The reactive sizes are alternatively used in the engine sizing of thepaper products to be used according to the invention as substratematerial for the packaging materials. They are used in particular whenpackaging materials having particularly good edge penetration aredesired. They are then employed in amounts which are usually requiredfor the production of sized paper products, e.g. from 0.1 to 2.0,preferably from 0.1 to 0.5, % by weight, based on dry cellulose fibers.For example, from 0 to 90, preferably from 50 to 90, parts by weight ofreactive sizes are used per 100 parts by weight of polymer size. Ifmixtures of a polymer size dispersion and of an aqueous dispersion of areactive size are used, the mixtures comprise, for example, from 5 to50, preferably from 10 to 30, % by weight, based in each case on thepolymer content, of polymer (100% strength).

If reactive sizes are used together with a polymer size, the reactivesizes, preferably alkylketene dimer dispersions, can first be added tothe paper stock and then the polymer size dispersions can be metered.However, the alkylketene dimer dispersion and at least one polymer sizedispersion can also be added simultaneously to the paper stock and thelatter then drained with sheet formation, or a mixture of a reactivesize, such as at least one alkylketene dimer dispersion, and at leastone polymer size dispersion is added to the paper stock and the latteris then drained with sheet formation.

The polymer sizes can of course also be used as surface sizes byapplying them, for example with the aid of a size press, to the surfaceof the paper or spraying them onto the surface of the paper.

The draining of the paper stock is additionally effected in the presenceof a retention aid. Apart from anionic retention aids or nonionicretention aids, such as polyacrylamides, cationic polymers arepreferably used as retention aids and as drainage aids. A significantimprovement in the runability of the paper machines is achieved thereby.Cationic retention aids which may be used are all products commerciallyavailable for this purpose. These are, for example, cationicpolyacrylamides, polydiallyldimethylammonium chlorides,polyethylenimines, polyamines having a molar mass of more than 50 000,polyamines which, if appropriate, are modified by grafting-on ofethylenimine, polyetheramides, polyvinylimidazoles,polyvinylpyrrolidines, polyvinylimidazolines,polyvinyltetrahydropyridines, poly(dialkylaminoalkyl vinyl ethers),poly(diallkylaminoalkyl (meth)acrylates) in protonated or inquarternized form, and polyamidoamines obtained from a dicarboxylicacid, such as adipic acid, and polyalkylenepolyamines, such asdiethylenetriamine, which are grafted with ethylenimine and crosslinkedwith polyethylene glycol dichlorohydrin ethers according to DE-B-24 34816, or polyamidoamines which have been reacted with epichlorohydrin togive water-soluble condensates, and copolymers of acrylamide ormethacrylamide and dialkylaminoethyl acrylates or methacrylates, forexample copolymers of acrylamide arid dimethylaminoethyl acrylate in theform of the salt with hydrochloric acid or in a form quaternized withmethyl chloride. Further suitable retention aids are microparticlesystems comprising cationic polymers, such as cationic starch and finelydivided silica, or comprising cationic polymers, such as cationicpolyacrylamide, and bentonite.

The cationic polymers which are used as retention aids have, forexample, Fikentscher K values of at least 140 (determined in 5% strengthaqueous sodium chloride solution at a polymer concentration of 0.5% byweight, a temperature of 25° C. and a pH of 7). They are preferably usedin amounts of from 0.01 to 0.3% by weight, based on dry cellulosefibers.

If appropriate, at least one cationic polymer may also be added to theaqueous slurry of cellulose fibers, in addition to the abovementionedsubstances. Examples of cationic polymers are polymers comprisingvinylamine units, polymers comprising vinylguanidine units, polymerscomprising dialkylaminoalkyl(meth)acrylamide units, polyethylenimines,polyamidoamines grafted with ethylenimine and/orpolydiallyidimethylammonium chlorides. The amount of cationic polymersis, for example, from 0.001 to 2.0, preferably from 0.01 to 0.1, % byweight, based on dry cellulose fibers.

Polymers comprising vinylamine units are known, cf. U.S. Pat. No.4,421,602, U.S. Pat. No. 5,334,287, EP-A-0 216 387, U.S. Pat. No.5,981,689, WO-A-00/63295 and U.S. Pat. No. 6,121,409. They are preparedby hydrolysis of open-chain polymers comprising N-vinylcarboxamideunits. These polymers are obtainable, for example, by polymerization ofN-vinylformamide, N-vinyl-N-methylformamide, N-vinylacetamide,N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide andN-vinylpropionamide. Said monomers can be polymerized either alone ortogether with other monomers.

Suitable monoethylenically unsaturated monomers which are copolymerizedwith the N-vinylcarboxamides are all compounds copolymerizabletherewith. Examples of these are vinyl esters of saturated carboxylicacids of 1 to 6 carbon atoms, such as vinyl formate, vinyl acetate,vinyl propionate and vinyl butyrate, and vinyl ethers, such as C₁- toC₆-alkyl vinyl ethers, e.g. methyl or ethyl vinyl ether. Furthersuitable comonomers are esters, amides and nitriles of ethylenicallyunsaturated C₃- to C₆-carboxylic acids, for example methyl acrylate,methyl methacrylate, ethyl acrylate and ethyl methacrylate, acrylamideand methacrylamide and acrylonitrile and methacrylonitrile.

Further suitable carboxylic esters are derived from glycols orpolyalkylene glycols, in each case only one OH group being esterified,e.g. hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylacrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate,hydroxybutyl methacrylate and monoesters of acrylic acid withpolyalkylene glycols having a molar mass of from 500 to 10 000. Furthersuitable comonomers are esters of ethylenically unsaturated carboxylicacids with amino alcohols, for example dimethylaminoethyl acrylate,dimethylaminoethyl methacrylate, diethylaminoethyl acrylate,diethylaminoethyl methacrylate, dimethylaminopropyl acrylate,dimethylaminopropyl methacrylate, diethylaminopropyl acrylate,dimethylaminobutyl acrylate and diethylaminobutyl acrylate. The basicacrylates can be used in the form of the free bases, of the salts withmineral acids, such as hydrochloric acid, sulfuric aicd or nitric acid,of the salts with organic acids, such as formic acid, acetic acid,propionic acid or the sulfonic acids, or in quaternized form. Suitablequaternizing agents are, for example, dimethyl sulfate, diethyl sulfate,methyl chloride, ethyl chloride and benzyl chloride.

Further suitable comonomers are amides of ethylenically unsaturatedcarboxylic acids, such as acrylamide, methacrylamide and N-alkylmono-and diamides of monoethylenically unsaturated carboxylic acids havingalkyl radicals of 1 to 6 carbon atoms, e.g. N-methylacrylamide,N,N-dimethylacrylamide, N-methylmethacrylamide, N-ethylacrylamide,N-propylacrylamide and tert-butylacrylamide and basic (meth)acrylamides,e.g. dimethylaminoethylacrylamide, dimethylaminoethyl methacrylamide,diethylaminoethylacrylamide, diethylaminoethylmethacrylamide,dimethylaminopropylacrylamide, diethylaminopropylacrylamide,dimethylaminopropylmethacrylamide and diethylaminopropylmethacrylamide.

N-Vinylpyrrolidone, N-vinylcaprolactam, acrylonitrile,methacrylonitrile, N-vinylimidazole and substituted N-vinylimidazoles,e.g. N-vinyl-2-methylimidazole, N-vinyl4-methylimidazole,N-vinyl-5-methylimidazole and N-vinyl-2-ethylimidazole, andN-vinylimidazolines, such as N-vinylimidazoline,N-vinyl-2-methylimidazoline and N-vinyl-2-ethylimidazoline, arefurthermore suitable as comonomers. Apart from being used in the form ofthe free bases, N-vinylimidazoles and N-vinylimidazolines are alsoemployed in a form neutralized with mineral acids or organic acids or inquaternized form, the quaternization preferably being carried out withdimethyl sulfate, diethyl sulfate, methyl chloride or benzyl chloride.Diallyldialkylammonium halides, e.g. diallyldimethylammonium chloride,are also suitable.

The copolymers comprise for example,

-   -   from 95 to 5, preferably from 90 to 10, mol % of at least one        N-vinylcarboxamide and    -   from 5 to 95, preferably from 10 to 90, mol % of other        monoethylenically unsaturated monomers copolymerizable therewith        incorporated in the form of polymerized units. The comonomers        are preferably free of acid groups.

Polymers comprising vinylamine units are preferably prepared startingfrom homopolymers of N-vinylformamide or from copolymers which areobtainable by copolymerization of

-   -   N-vinylformamide with    -   vinyl formate, vinyl acetate, vinyl propionate, acrylonitrile,        N-vinylcaprolactam, N-vinylurea, N-vinylpyrrolidone or C₁- to        C₆-alkyl vinyl ethers        and subsequent hydrolysis of the homopolymers or of the        copolymers with formation of vinylamine units from the        polymerized N-vinylformamide units, the degree of hydrolysis        being, for example, from 5 to 100, preferably from 70 to 100,        mol %. The hydrolysis of the polymers described above is        effected by the action of acids, bases or enzymes by known        methods. When acids are used as the hydrolyzing agent,        vinylamine units of the polymers are present as ammonium salt,        whereas the free amino groups form in the case of the hydrolysis        with bases.

In most cases, the degree of hydrolysis of the homo- and copolymers isfrom 80 to 95 mol %. The degree of hydrolysis of the homopolymers isequivalent to the content of vinylamine units in the polymers. In thecase of copolymers which comprise vinyl esters in the form ofpolymerized units, hydrolysis of the ester groups with formation ofvinyl alcohol units may occur in addition to the hydrolysis of theN-vinylformamide units. This is the case in particular when thehydrolysis of the copolymers is carried out in the presence of sodiumhydroxide solution. Acrylonitrile incorporated in the form ofpolymerized units is likewise chemically changed in the hydrolysis.Here, for example, amido groups or carboxyl groups form. The homo- andcopolymers comprising vinylamine units may if appropriate comprise up to20 mol % of amidine units, which are formed, for example, by reaction offormic acid with two neighboring amino groups or by intramolecularreaction of an amino group with a neighboring amido group, for exampleof N-vinylformamide incorporated in the form of polymerized units. Themolar masses M_(W) of the polymers comprising vinylamine units are, forexample, from 500 to 10 million, preferably from 1 000 to 5 million(determined by light scattering). This molar mass range corresponds, forexample, to K values of from 5 to 300, preferably from 10 to 250(determined according to H. Fikentscher in 5% strength aqueous sodiumchloride solution at 25° C. and a polymer concentration of 0.5% byweight).

The polymers comprising vinylamine units are preferably used insalt-free form. Salt-free aqueous solutions of polymers comprisingvinylamine units can be prepared, for example, from the salt-containingpolymer solutions described above with the aid of ultrafiltrationthrough suitable membranes at cut-offs of, for example, from 1 000 to500 000, preferably from 10 000 to 300 000, Dalton. The below-describedaqueous solutions of other polymers comprising amino and/or ammoniumgroups can also be obtained in salt-free form with the aid ofultrafiltration.

Derivatives of polymers comprising vinylamine units can also be used ascationic polymers. Thus, it is possible, for example, to prepare amultiplicity of suitable derivatives from the polymers comprisingvinylamine units by amidation, alkylation, sulfonamide formation, ureaformation, thiourea formation, carbamate formation, acylation,carboxymethylation, phosphonomethylation or Michael addition of theamino groups of the polymer. Of particular interest here areuncrosslinked polyvinylguanidines, which are obtainable by reaction ofpolymers comprising vinylamine units, preferably polyvinylamines, withcyanamide (R¹R²N-CN, where R¹ and R² are H, C₁- to C₄-alkyl, C₃- toC₆-cycloalkyl, phenyl, benzyl, alkyl-substituted phenyl or naphthyl),cf. U.S. Pat. No. 6,087,448, column 3, line 64 to column 5, line 14.

The polymers comprising vinylamine units also include hydrolyzed graftpolymers of, for example, N-vinylformamide on polyalkylene glycols,polyvinyl acetate, polyvinyl alcohol, polyvinylformamides,polysaccharides, such as starch, oligosaccharides or monosaccharides.The graft polymers are obtainable by subjecting, for example,N-vinylformamide to free radical polymerization in an aqueous medium inthe presence of at least one of said grafting bases, if appropriatetogether with other copolymerizable monomers, and then hydrolzying thegrafted-on vinylformamide units in a known manner to give vinylamineunits.

Suitable cationic polymers are also polymers ofdialkylaminoalkyl(meth)acrylamides. Suitable monomers for thepreparation of such polymers are, for example,dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide,dimethylaminopropylacrylamide, dimethylaminopropylmethacrylamide,diethylaminoethylacrylamide, diethylaminoethylmethacrylamide anddiethylaminopropylacrylamide. These monomers can be used in the form ofthe free bases, of the salts with inorganic or organic acids or inquaternized form in the polymerization. They can be subjected to freeradical polymerization to give homopolymers or, together with othercopolymerizable monomers, to give copolymers. The polymers comprise, forexample, at least 30, preferably at least 70, mol % of said basicmonomers incorporated in the form of polymerized units.

Further suitable cationic polymers are polyethylenimines which can beprepared, for example, by polymerization of ethylenimine in aqueoussolution in the presence of acid-eliminating compounds, acids or Lewisacids as a catalyst. Polyethylenimines have, for example, molar massesof 2 million, preferably from 200 to 1 000 000. Polyethylenimines havingmolar masses of from 500 to 750 000 are particularly preferably used.The polyethylenimines can, if appropriate, be modified, for example,alkoxylated, alkylated or amidated. They can also be subjected to aMichael addition or a Stecker synthesis. The polyethyleniminederivatives obtainable thereby are likewise suitable as cationicpolymers.

Polyamidoamines grafted with ethylenimine and obtainable, for example,by condensation of dicarboxylic acids with polyamines and subsequentgrafting-on of ethylenimine are also suitable. Suitable polyamidoaminesare obtained, for example, by reacting dicarboxylic acids of 4 to 10carbon atoms with polyalkylenepolyamines which comprise from 3 to 10basic nitrogen atoms in the molecule. Examples of dicarboxylic acids aresuccinic acid, maleic acid, adipic acid, glutaric acid, suberic acid,sebacic acid and terephthalic acid. In the preparation of thepolyamidoamines, mixtures of dicarboxylic acids may also be used, as maymixtures of a plurality of polyalkylenepolyamines. Suitablepolyalkylenepolyamines are, for example, diethylenetriamine,triethylenetetramine, tetraethylenepentamine, dipropylenetriamine,dipropylenetetramine, dihexamethylenetriamine,aminopropylethylenediamine and bisaminopropylethylenediamine. For thepreparation of the polyamidoamines, the dicarboxylic acids andpolyalklenepolyamines are heated to relatively high temperatures, forexample to temperatures in the range from 120 to 220° C., preferablyfrom 130 to 180° C. The water formed during the condensation is removedfrom the system. In the condensation, lactones or lactams of carboxylicacids of 4 to 8 carbon atoms can, if appropriate, also be used. Forexample, from 0.8 to 1.4 mol of a polyalkylenepolyamine are used permole of a dicarboxylic acid. These polyamidoamines are grafted withethylenimine. The grafting reaction is carried out, for example, in thepresence of acids or Lewis acids, such as sulfuric acid or borontrifluoride etherates, at, for example, from 80 to 100° C. Compounds ofthis type are described, for example, in DE-B-24 34 816.

The optionally crosslinked polyamidoamines, which are, if appropriateadditionally grafted with ethylenimine before the crosslinking, are alsosuitable as cationic polymers. The crosslinked polyamidoamines graftedwith ethylenimine are water-soluable and have, for example, an averagemolecular weight M_(W) of from 3 000 to 2 million Dalton. Conventionalcrosslinking agents are, for example, epichlorohydrin or bischlorohydrinethers of alkylene glycols and polyalkylene glycols.

Other suitable cationic polymers are polyallylamines. Polymers of thistype are obtained by homopolymerization of allylamine, preferably in theform neutralized with acids, or by copolymerization of allylamine withother monoethylenically unsaturated monomers which are described aboveas comonomers for N-vinylcarboxainides.

In addition, water-soluble crosslinked polyethylenimines which areobtainable by reacting polyethylenimines with crosslinking agents, suchas epichlorohydrin or bischlorohydrin ethers of polyalkylene glycolshaving from 2 to 100 ethylene oxide and/or propylene oxide units andalso have free primary and/or secondary amino groups are suitable.Amidic polyethylenimines which are obtainable, for example, by amidationof polyethylenimines with C₁- to C22-monocarboxylic acids are alsosuitable. Further suitable cationic polymers are alkylatedpolyethylenimines and alkoxylated polyethylenimines. In thealkoxylation, for example, from 1 to 5 ethylene oxide or propylene oxideunits are used per NH unit in the polyethylenimine.

The abovementioned catonic polymers have, for example, K values of from8 to 300, preferably from 15 to 180 (determined according to H.Fikentscher in 5% strength aqueous sodium chloride solution at 25% andat a polymer concentration of 0.5% by weight). At a pH of 4.5, theyhave, for example, a charge density of at least 1, preferably at least4, meq/g of polyelectrolyte.

Preferred cationic polymers are polymers comprising vinylamine units andpolyethylenimines. Examples of these are:

vinylamine homopolymers, from 10 to 100% hydrolyzed polyvinylformamides,partly or completely hydrolyzed copolymers of vinylformamide and vinylacetate, vinyl alcohol, vinylpyrrolidone or acrylamide, in each casehaving molar masses of 3 000-2 000 000, and

polyethylenimines, crosslinked polyethylenimines or amidatedpolyethylenimines, which have in each case molar masses of from 500 to 3000 000.

The polymer content of the aqueous solution is, for example, from 1 to60, preferably from 2 to 15, in general from 5 to 10, % by weight.

Cardboard is usually produced by draining a slurry of cellulose fibers.The use of kraft pulp is preferred. Furthermore, the use of TMP and CTMPis of particular interest. The pH of the cellulose fiber slurry is, forexample, from 4 to 8, preferably from 6 to 8. The drainage of the paperstock can be carried out batchwise or continuously on a paper machine.Cationic polymer, engine size and retention aid can be added in anychosen sequence. However, a procedure in which first the retention aidand then the cationic polymer, preferably polyvinylamine, and then atleast one reactive size, such as alkylketene dimer, alkyl- oralkenylsuccinic anhydride, in combination with an aluminum compound or amixture of these sizes and a polymer size are added to the aqueouscellulose fiber slurry is preferred. According to another embodiment,first at least one polymer size, then the retention aid and finally thecationic polymer are metered.

In the production of the paper products to be used according to theinvention, other assistants usually suitable may be present, for examplefixing agents, dyes, bactericides and dry and/or wet strength agents forpaper.

After the drainage of the paper stock and drying of the paper product,an engine sized cardboard having a basis weight of from 80 to 400,preferably from 120 to 220, g/m² is obtained. The cardboard is laminatedon one or both sides with a plastics film or metal foil, such asaluminum foil.

Suitable plastics films may be produced from polyethylene,polypropylene, polyamide or polyester. The films or foils can be bondedto the sized paper products, for example, with the aid of an adhesive.In such cases, films or foils which are coated with an adhesive aregenerally used and the laminate is pressed. However, the surface of thesized paper products can also be coated with an adhesive and the film orfoils then applied to one or both sides and the resulting laminatepressed. However, the films or foils can also be processed with thecardboard directly by the action of heating and pressure to give alaminate, from which the suitable structures for production of thepackaging for liquids are then cut out. The packagings are preferablyused in the food sector, for example for packing beverages, such asmineral water, juices or milk, or for the production of beveragevessels, such as cups. In the case of these packagings, it is importantthat they have good edge penetration, i.e. the cardboard should absorbvery little or virtually no liquid. The adhesion of films or foils tothe paper products sized with polymer sizes is better than that of filmsor foils to paper products which are sized exclusively with alkylketenedimers.

In the examples which follow, percentages are by weight, unless evidentotherwise from the context. The K values were determined according to H.Fikentscher, Cellulose-Chemie 13 (1932), 58-64 and 71-74, in 5% strengthaqueous sodium chloride solution at 25° C. and a pH of 7 at a polymerconcentration of 0.5% by weight. The molar masses M_(W) of the polymerswere measured by light scattering.

EXAMPLE

Determination of the Edge Penetration

The cardboard produced in each case was laminated on both sides with apolyethylene adhesive tape. The thickness of the cardboard was thendetermined. Test strips measuring 25×75 mm were then cut from thecardboard and weighed in each case. In order to determine the edgepenetration, the test strips were dipped in a bath which comprised a 30%strength hydrogen peroxide solution thermostated at 70° C. The teststrips were removed from the bath after a residence time of 10 minutes.Excess hydrogen peroxide was absorbed by means of filter paper. The teststrips were once again weighed. The edge penetration in kg/m² was thencalculated from the increase in weight.

Ink Flotation Time

The ink flotation time (measured in minutes) is the time which a testink requires according to DIN 53126 for 50% strike-through through atest sheet.

Cobb Value

The determination was carried out according to DIN 53 132 by storing thepaper sheets for a period of 60 seconds in water. The water absorptionis stated in g/m².

Examples 1 to 6

0.75%, based in each case on dry paper stock, of a cationic starch(Solvitose BPN) was added as a retention aid to a paper stock having aconsistency of 10 g/l and comprising 100% unbleached pine sulfate pulphaving a freeness of 20° SR (Schopper-Riegler), and the pH of themixture was brought to 7. In each case the amounts of stearyldiketenestated in the table, in the form of an aqueous dispersion (Basoplast®4118MC), and an aqueous dispersion of the polymer sizes likewise statedin table 1 were then metered. The fiber slurries were thoroughly mixedin each case and drained on a Rapid-Köthen sheet former. Sheets having abasis weight of 150 g/m² were obtained.

The following polymer sizes were used:

Polymer size A: Basoplast® 250D (aqueous dispersion of a copolymer,prepared by emulsion polymerization of acrylonitrile and n-butylacrylate in the presence of degraded cationic starch as an emulsifierand hydrogen peroxide as an initiator).

Polymer size B: Basoplast® 265D (aqueous dispersion of a copolymer,prepared by emulsion polymerization of styrene and n-butyl acrylate inthe presence of degraded cationic starch as an emulsifier and hydrogenperoxide as an initiator).

Polymer size C: Basoplast® PR8172 (aqueous dispersion of a copolymer,prepared by emulsion polymerization of styrene and n-butyl acrylate inthe presence of cationic starch as an emulsifier and hydrogen peroxideas an initiator). TABLE 1 Example Stearyldiketene [%], Amount of polymersize [%], No. based on dry fibers Type based on dry fibers 1 0.1 A 0.252 0.1 A 0.5 3 0.1 B 0.25 4 0.1 B 0.5 5 0.1 C 0.25 6 0.1 C 0.5

The sheets were then dried on a steam-heated drying cylinder at 90° C.to a water content of 6-10%. After the drying, the Cobb value of thesheets was determined. The sheets were then laminated on both sides withan adhesive tape polyethylene having a density of 0.918 g/cm³ (heatingof the laminate under pressure to 30° C.). The edge penetration of thethree-layer laminate was then determined. The results are shown in table3.

Comparative Examples 1 to 4

0.75%, based in each case on dry paper stock, of a cationic starch(Solvitose BPN) was added as a retention aid to a paper stock having aconsistency of 10 g/l and comprising 100% unbleached pine sulfate pulphaving a freeness of 20° SR (Schopper-Riegler), and the pH of themixture was brought to 7. In each case the amounts of stearyldiketeneshown in table 2 were then metered in the form of an aqueous dispersion(Basoplast® 4118MC). Thereafter, in each case the aqueous fiber slurrieswere thoroughly mixed and were drained on a Rapid-Köthen sheet former togive a paper product having a basis weight of 150 g/m². TABLE 2Comparative [%] stearyldiketene, example based on dry fibers 1 0.1 2 0.23 0.35 4 0.60

The sheets were then dried on a steam-heated drying cylinder at 90° C.to a water content of 6-10%. After the drying, the Cobb value of thesheets was determined. The sheets were then adhesively bonded on bothsides to a polyethylene adhesive tape (pressing of the laminate underpressure). The edge penetration of the three-layer laminate with respectto hydrogen peroxide was then determined. The results are shown in table3. TABLE 3 Edge penetration [kg/m²] Cobb 60 sec for (peroxides) forlaminated cardboard cardboard Sample according to example 1 20 10.9 2 2110.6 3 23 6.6 4 22 4.6 5 20 10.2 6 23 11.3 Sample according tocomparative example 1 20 12.1 2 24 8.6 3 20 7.2 4 21 5.3

1. A packaging material comprising an at least two-layer laminate ofsized paper or sized cardboard and at least one water-impermeable filmor foil for producing containers for packaging liquids, wherein thepaper or the cardboard is in each case sized with a polymer size.
 2. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard is in each case engine sized with a polymer size.
 3. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard is in each case surface sized with a polymer size.
 4. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard is additionally sized in the presence of aqueous dispersionsof reactive sizes and/or combinations of rosin size and alum.
 5. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard is obtainable by successive addition of aqueous alkylketenedispersions and aqueous polymer size dispersions to the paper stock anddrainage of the paper stock on the wire of a paper machine.
 6. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard is obtainable by simultaneous addition of aqueous alkylketenedimer dispersions and aqueous polymer size dispersions to the paperstock and drainage of the paper stock on the wire of a paper machine. 7.The packaging material as claimed in claim 1, wherein the paper or thecardboard is obtained by sizing with a size mixture comprising anaqueous polymer size dispersion and an aqueous alkylketene dimerdispersion.
 8. The packaging material as claimed in claim 1, wherein thepaper or the cardboard is additionally sized in the presence of cationicpolymers.
 9. The packaging material as claimed in claim 1, wherein thepaper or the cardboard is in each case laminated on both sides with awater-impermeable plastics film and/or metal foil.
 10. The packagingmaterial as claimed in claim 1, wherein the paper or the cardboard islaminated on one or both sides with a film of polyethylene,polypropylene, copolymer of ethylene and propylene, polyester, polyvinylalcohol, copolymer of ethylene and vinyl acetate, copolymer of ethyleneand vinyl alcohol, or polyamide and/or an aluminum foil.
 11. Thepackaging material as claimed in claim 1, wherein the paper or thecardboard has a basis weight of from 80 to 400 g/m² and is laminated onboth sides with a polyethylene film.
 12. A method for producing acontainer for packaging liquids comprising producing a paper productwhich is obtained by (i) engine sizing of a paper stock comprising anaqueous slurry of cellulose fibers with at least one polymer size orwith a polymer size and an aqueous dispersion of an alkylketene dimer ora mixture thereof in the presence of a retention aid and, optionally, ofa water-soluble aluminum compound and, optionally, at least one cationicpolymer, (ii) drainage of the paper stock on the wire of a papermachine, (iii) drying of the paper product and (iv) lamination of thepaper product on one or both sides with a plastics film or metal foil.